1. Field of the Invention
The present invention relates to a nonvolatile memory device. More specifically, the present invention relates to a magnetic random access memory with write and read circuits using magnetic tunnel junction (MTJ) devices.
2. Description of the Related Art
A nonvolatile magnetic random access memory is an array of individual magnetic memory cells. Each memory cell includes a magnetic tunnel junction (MTJ) device. FIG. 1 illustrates the basic structure of a MTJ device in a conventional magnetic memory cell. Referring initially to FIG. 1, each MTJ device includes a pinned ferromagnetic layer 12, the magnetization direction of which is fixed, an antiferromagnetic layer 11, for pinning the magnetization of the pinned ferromagnetic layer 12 by use of an antiferromagnetic coupling, a free ferromagnetic layer 14, the magnetization direction of which is free to rotate parallel or antiparallel to the fixed magnetization direction of the pinned ferromagnetic layer 12, and an insulating tunnel barrier 13 that is placed between the pinned ferromagnetic layer 12 and the free ferromagnetic layer 14. FIG. 2 is a perspective view that illustrates the structure of a magnetic random access memory using a conventional MTJ. (Such a conventional device is disclosed in U.S. Pat. No. 5,640,343, for example). In the magnetic memory array shown in FIG. 2, the magnetic state of a free layer of the MTJ may depend on a magnetic field induced by electric current that flows through a word line and a bit line. Accordingly, this conventional device has a problem in that the direction of a magnetic field created in the MTJ of FIG. 3A is not formed in parallel or antiparallel to the fixed magnetization of a pinned ferromagnetic layer, as illustrated in FIGS. 3B and 3C.
To solve the above problem, it is a feature of the present invention to provide a magnetic random access memory with read and write circuits using magnetic tunnel junction (MTJ) devices, wherein the magnetic random access memory can effectively change the magnetization direction of a free ferromagnetic layer in the MTJ device formed at the intersection point of word line and bit line to thereby read and write the magnetic state of the free ferromagnetic layer.
In an effort to satisfy this and other features of the present invention, there is provided a magnetic random access memory with read and write circuits using MTJ devices including word lines arranged in stripes at a regular interval, read bit lines and write bit lines that are arranged in stripes in a direction intersecting the word lines and are parallel to each other, magnetic tunnel junction devices formed to be in contact with the word lines and read bit lines at the cross points of the two lines, and current bypass paths that are coupled to the word lines and the write bit lines and are formed for allowing the current to bypass the side and the bottom of each magnetic tunnel junction device.
The current bypass paths include a via hole path, which is coupled to the word line and passes the magnetic tunneling junction devices in a vertical and downward direction, and a base path, which is coupled to the write bit lines and the via hole path and passes below the read bit line in contact with the magnetic tunneling junction device.
Each MTJ includes a pinned ferromagnetic layer, the magnetization direction of which is fixed, an antiferromagnetic layer for pinning the magnetization direction of the pinned ferromagnetic layer by use of an antiferromagnetic coupling, a free ferromagnetic layer, the magnetization direction of which is free to change in a direction parallel or antiparallel to the fixed magnetization direction of the pinned ferromagnetic layer, and an insulating tunnel barrier between the pinned ferromagnetic layer and free ferromagnetic layer.
The above and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.